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Comparison of Multiple Pulse Sequences for MRI Based Gel Dosimetry

B Maraghechi , H Gach , D Yang , H Li*, Washington University School of Medicine, St Louis, MO


(Tuesday, 7/31/2018) 3:45 PM - 4:15 PM

Room: Exhibit Hall | Forum 7

Purpose: Polymer gel dosimeters are commonly scanned with Magnetic Resonance Imaging (MRI) after being irradiated. However, high cost and limited accessibility of MRI in clinics are some of the challenges in gel dosimetry. Utilizing pulse sequences that results in a comparable dosimetric performance but with shorter scan time can overcome some of these challenges. The objective of this study was to compare the relative dose uncertainty obtained from scanning a polymer gel dosimeter with multiple pulse sequences with different acquisition times.

Methods: A BANG polymer gel dosimeter was used in this study. The gel was irradiated by three beams of 3 cm × 3 cm field size with 432 and 720 MU. The gel was scanned with a Philips 1.5 T scanner using multiple pulse sequences: Spin Echo (SE), Carr-Purcell-Meiboom-Gill (CPMG), and a fast T2 mapping technique (k-t-T2). The pixel size was 1.5 × 1.5 mm² with a 5 mm slice thickness and 30 slices were acquired. The field of view was 180 × 180 × 150 mm³ and the repetition time was 10238 ms for the k-t-T2 and 8000 ms for the SE and CPMG sequences. R2 maps were calculated for each technique and registered to the calculated dose maps. The dose uncertainty was derived from dose versus R2 curves.

Results: As the dose was increased from 2 Gy to 7.5 Gy the dose uncertainty decreased from 18% to 4.5%, 7.5% to 1.7%, and 10.4% to 3.1% using the SE (48 min), CPMG (49 min) and k-t-T2 (25 min), respectively.

Conclusion: The CPMG pulse sequence yields the lowest dose uncertainty but takes the longest time. The dose uncertainty obtained from the fast T2 mapping technique (k-t-T2) is on average 1.8% higher than the CPMG technique but it is two times faster.


Gel Dosimeter, MRI, Quality Assurance


TH- Radiation dose measurement devices: 3D solid gel/plastic

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